The present invention relates to fluid drug delivery devices and, in particular, it concerns a portable insulin delivery device.
There are known portable insulin delivery devices, commonly referred to as insulin pumps, that generally consist of a pump mechanism, an insulin container, a processor, and a power source for the processor and pump mechanism. The pump mechanisms of prior art generally use motor driven push rods to push a piston into the insulin containment region of the insulin container, thus forcing the insulin into a delivery tube and therefore into the patient. The inventions of prior art have gone to great lengths to devise variation of the motor driven push rod and piston assembly that is accurate, reliable, and space efficient. Disclosures representative of this case of devices will be found in U.S. Pat. Nos. 6,248,093, 5,637,095, 5,097,122, and 5,505,709. Devices based on this configuration suffer from two inherent problems, the motor and the push rod and piston assembly, as discussed in the following paragraphs.
The amount of insulin delivered to the patient is therefore controlled by the speed at which the motor turns (RPM's) and the amount of time the motor is turning. The accuracy of insulin delivery is, then, dependent on the reliability and accuracy of the motor. Variations on RPM's will cause variations in the amount of insulin delivered to the patient. Due to a limited power supply the motor is turned on and off at preset intervals. Even when the system is operating properly, the medication is delivered in “spurts” and the delivery rate is determined as an average over time.
As the motor turns, it moves a push rod, which in turn moves a piston that forces the insulin out of the container. The seal between the piston and the side of the container must be very tight in order to prevent leakage of insulin. A side effect of this tightness is the tendency of the piston to move forward at an uneven rate. That is to say, that the piston may stick and then jump forward. This uneven movement of the piston causes uneven delivery of the insulin to the patient.
The prior art has developed elaborate devices to detect and respond to occlusion and other flow rate or system malfunctions as is demonstrated in U.S. Pat. Nos. 5,097,122, 5,462,525, 4,619,653, and 5,647,853. In cases of occlusion, most commonly these devices allow the motor to continue to push against the blockage. Due the limitation of the motor, and since this happens only in cases of full occlusion, this is not a very satisfactory solution. Further, if the blockage is opened, the pressure built up in the container and delivery tube is released through the tube, thereby forcing a possibility dangerously larger than prescribed dose of insulin into the patient. One proactive approach to occlusion includes the use of “inert” cleaning fluid being pumped through the device and into the patient.
There is therefore a need for a portable insulin delivery device that is able to deliver the insulin at a substantially consistent dosage rate, quickly detect flow rate malfunction, overcome blockage with substantially no affect on the prescribed dosage or the use of non-medicative cleaning fluids, and has very low energy requirements. It would be preferable if the device had low power requirements, and was more compact and economical than devices currently in use.